1. Field of the Invention
The present invention relates to a drive element for use with a driver. The invention relates in particular to a construction of an entry surface formed at the entry end of a drive bore formed in the drive element.
2. Description of the Prior Art
A drive element for use with a driver typically comprises a body within which is formed a drive bore including a central axis, and a plurality of intersecting flat side surfaces parallel to the central axis for mateably receiving a drive lug of a driver which includes a corresponding plurality of intersecting flat side surfaces and a resiliently retractable ball projecting from one of the side surfaces. In order to facilitate the depression of the ball as the drive lug is inserted into the drive bore, current drive elements comprise a frustoconical entry surface which is formed at an entry end of the drive bore.
The entry surface has been formed at a relatively large acute angle with respect to the central axis of the drive bore to minimize the axial distance which the entry surface extends into the drive bore. The large angle, however, is disadvantageous since it provides only a small lateral component of force against the ball in order to retract it, thereby requiring a large axial force to insert the drive lug in the drive bore.
If, alternatively, the entry surface is formed at a small angle with respect to the central axis of the drive bore to increase the lateral component of force which is applied against the ball in order to retract it, then the entry surface extends too far axially into the drive bore, thereby unduly decreasing the portion of the drive bore which is available for driving engagement with the drive lug.